Remote control system



NOV- 26, 1946- W. F. WOLFNER, D

REMOTE CONTROL SYSTEM Filed July s1 www .W A w a :m11 XIII :IB-hill llllll .Il llMmNdl-Inll Il Jil inl-Inl] Il lllll'l-ll lilill .Il Illllllrtll'billl Il; f El. I

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Patented Nov. 26, 1946 REMOTE coN'rnoL SYSTEM William F; Weltner, II,Philadelphia, Pa., assigner to Radio Corporation of America, acorporation of Delaware Application July 31, 1942, Serial No. 452,984

(ci. 11a-239) 8 Claims. \1

This invention relates to remote lcontrol systems and more particularlyto electrical followup systems for driving a controlled device, forexample a relatively heavy object such as a searchlight, a gun, or aradioantenna, to a position corresponding to that of a controllingdevice having relatively small torque capability, such as a handoperated controller or a sensitive instrument. i

In this type of system, the control is accomplished by lderiving avoltage, hereinafter referred to as a displacement signal, related inmagnitude to the diierence in angular position between the controllingdevice and the controlled device and operating an electric motor inaccordance with said voltage in4 such a way as to eiect zero differenceof positions. Numerous systems of this general type have been devised,and it has been found that it is usuallyY necessary to provide more crless elaborate means to prevent over-running and reversal of the drivingmotor at the point of positional agreement, corresponding to zerocontrol signal. This over-running and reversal may result in sustainedoscillation of the driven member about a position corresponding to thatof the control device. Such oscillation is called hunting. Similarly,the driven member will hunt during motion of the control device,increasing and decreasing in speed above and below that of the controldevice at a rate determined by the sensitivity of the system to angulardifferences in position, and the inertia and friction in the drivenload. Hunting may be excited by the sudden application or removal ofexternal force or resistance to motion on the' driven load, or by suddenstarting or stopping of the control device. v

Accordingly, it is an object oi' this invention to provide an improvedelectrical follow-up system; Another object' is to provide an improvedmethod of and means for deriving and combining the electrical componentsof the motor` con- A further object is the provision of improved meansfor utilizing said displacement signal to control the power input to anelectric motor. Still another object is the provision of an improvedmethod of and means ior preventing hunting of an electrical follow-upsystem. Another object is to provide a follow-up system requiring only arelatively small amount of equipment comprised of readily obtainablecomponents of standard design. A further object is to provide animproved method oi and means for controlling the operation of aninduction motor. These and other and incidental objects will becomeapparent to those skilled in the art upon consideration of the followingdescription, with reference to the accompanying drawing, which is aschematic circuit diagram of an embodiment of the invention.

Referring to the drawing, a movable body l such as a gun, search lightor radio antenna is designed to be oriented at an angle corresponding toa position of a control membersuch as a manually operable crank 3. Theobject l is connected to the rotor of a two ph se induction motor 5 bymechanical means, whic may include gearing, schematically indicated bythe dotted line l. The object l is also mechanically connected to therotor of a Selsyn transformer Il by means schematically indicated by adotted line 9. 'I'he transformer l l comprises a rotor having a singlewinding and three stator windings spaced 120 degrees apart. The statorwindings of the transformer Il are connected tocorresponding statorwindings of a similar transformer I3. The rotor of the transformer I3 ismechanically connected to the crank 3.

The induction motor 5 is energized from the A.C. lines 2 and 4 through acontrol circuit comprising transformers 31 and 39 and vacuum tubes 4Iand 43. The motor winding 53 is shunted by a condenser` through atransformer B9, in order to produce a quadrature phase relationbetweenthe currents through the windings 53 and 63. The transformer 69is employed to step up the voltage across the condenser 65 so that vacondenser of relatively small capacity may be used. The voltage ratio ofthe transformer B9 or the capacity of the condenser B5 is adjusted toproduce exact quadrature relation between the currents when the motor isat a standstill. lAs the motor 5 speeds up, the impedance of the phasewindings 53 and 63 change and currents through the windings do notremain in degree phase relation. This causes the emclency of the motorto decrease with increase in speed, allowing effective control over a.wide range of speeds by merely varying the impedance connected betweenthe motor and the line. The two windings are connected in series toprevent the motor from tending to operate single phase, which wouldcause instability because the motor would either stall or run at fullspeed.

The secondaries 45 and 41 of the transformer 31 andthe secondaries 49and 5l of the transformer 39 are connected to form a bridge circuit andthe winding G3 of the motor 5 is connected across one pair of conjugatepoints 59 and 8| on the bridge circuit. Power is supplied to bridge atthe other pair of conjugate points 55, 51 through the motor winding 55from the line 2, d. 'Ihe primaries 33 and 35 are connected in the plateto cathode circuits of the tubes 4I and 63, respectively. The internalimpedances of these tubes are reflected in the secondary windings d5 and67 and 139 and 5l, respectively. Thus, if the tube il is conducting andthe tube 133 is cut 01T, the windings 65 and il oifer low impedance tothe ow of current while the windings 49 and 5I offer high impedance, andthe terminal 'H of the winding 63 is effectively connected to the A.C.line 2 While the terminal 73 is connected "to the line d through thewinding 53, If tube d3 is conducting and tube di is cut o, theconnection to the winding $3 will be reversed. Thus, tubes il and i3 aremeans for simultaneously varying the impedances of the respectiveconjugate arms of the bridge circuit in opposite directions. Themagnitude of the current flowing through the motor windings depends uponthe degree to which either of the tubes lll or i3 is conductive. Thus itis possible to regulate the speed and direction of rotation of the motor5 by varying the grid voltages of the tubes il and 53.

One very important advantage in employing this type of control circuitlies in the fact that the power capability of the tubes il and needlonly be a fraction of that of the motor 5. The maximum powerdissipation in the control tubes occurs when half the line voltage isapplied to the motor and half isabsorbed in the control circuit. Whennearly all the voltage is across the motor,

the tube power dissipation is low, although the current is heavy, andthe motor is fully loaded. When the motor power is low, the voltageacross the control circuit is high, but very little current flows, sothe power dissipated in the control circuit is again relatively low.

Control voltages for the tubes il and i3 are derived from the rotor ofthe Selsyn transformer i3 which is connected through a transformer Si toa full wave grid controlled rectifier I5. The

voltage applied to the transformer 67 is proportional in magnitude tothe angular difference in position between the rotors of thetransformers i i and i3. Voltages from A.C. line 2, i is applied to therotor of the transformer I l and also to the control grids of therectifier tubes '15, Ti, i9 and 8l, through current limiting resistorsmi. The output of the rectier consists of unidirectional pulses whichare conducted through the lter 23 to a D.C. amplifier 25, thence to thecontrol grids of the tubes il and d3. The rectier output pulses willappear between the lead 8l? and one or the other of the leads 83 and 85,depending upon lwhether the rotor of thel transformer i3 leads or lagsthe rotor of the transformer ll, and the consequent polarity of therotor of transformer i3 with respect to the line 2, d. The averagemagnitude of the pulses will be proportional to tion, resulting insustained oscillations or hunting the angular difference in positionbetween the transformer rotors. The pulse polarity will be positive atlead 33 or 85, and negative at lead 8l. Thus a voltage is applied to thecontrol grid of either the tube di or the tube d3 causing the motor E torun at a speed proportional to the difierence in position of the controlmember. in the driven object and in the proper direction to reduce saiddifferences to zero.

The system as thus far described would not be satisfactory in operationfor the reason that the,

inertia of the driven object would cause the motor to overrun theposition of zero control signal, reverse the signal and overrun in theopposite direcf to the displacement.

of the system. This can be prevented by reducing the control signal toZero before the motor reaches its nal position: A voltage is added tothe signal, applied to the D.C. amplier 25, in the proper polarity tooppose the, displacement signal. This voltage is derived from arectifier 29 which is connected across the winding 63 of the motor 5.The opposing voltage is thus proportional to the terminal voltage of themotor and is indirectly related to the motor speed and torque as Well asto the control signal. Consider the motor 5 is an impedance Z, varyingin magnitude inversely with respect to the torque', and theconpredeterminedl voltage is applied to the input of.

the rectier. Y

Thus if the rotors of the transformer il and i3 are displaced relativeto each other, the initial signal reaching the tube H or Il?, isproportional However, as soon as the voltage across the motor winding 63increases above a predetermined threshold value the rectifier 29 startsto conduct and the control signal is reduced by an amount dependent uponthe terminal voltage ofthe motor. As the .transformer rotors approach aposition of agreement, the displacement signalhderived from the rotor oftransformer i3 is completely neutralized or balanced Iby the output ofthe rectifier 29 so that the energization of the motor 5 is reduced tozero before the driven object has reached its nal position.

If the threshold bias on the rectifier 29 is adjusted to the propervalue, the motor 5 and its load will coastv to the final position andstop without hunting.

If the system is operating with some particular value ofcontrol-impedance and there is a momentary increase or decrease of thetorque load, the feedback voltage is varied so as toincrease or decreasethe control signal and change the control impedance. Z' to conform tothe change in load.

Thus the invention has been described as an improved servo system. AnA.-C. signal proportional to the angular displacement between thecontrol and driven shafts is derived by means of Selsyn transformers.This signal is rectied and employed to control space discharge tubesconnected to act as a control impedance between a driving motor and apower source. To prevent hunting, an auxiliary control signal is derivedfrom the terminals of the driving motor, recti` ed, and applied througha threshold device to the control circuit, in opposition to therectified displacement signal.

I claim as my invention:

l. A follow-up system including an input shaft, an output shaft, a loadcoupled to said output shaft, means responsive to the angular positionsof said shafts to produce a displacement signal voltage having amagnitude proportional to the difference of said angular positions, amotor coupled to said output shaft and connected to a source ofelectrical energy through variable impedance means, means forcontrolling the impedance of said variable impedance means inresponse tocontrol signal voltage applied thereto, rectifier means with an inputcircuit connected to apower input circuit of said motor and an outputcircuit connected to said position-responsive means to add the output ofsaid rectifier means to said displacement signal voltage to produce acontrol signal voltage, means for applying said control signal voltageto said variable impedance controlling means, and means for applying atheshoid bias to said rectier means to prevent operation thereof exceptwhen the in- 'put to said rectiner means has a magnitude greater than a:Finite value predetermined in accordance with the frictional andinertia characteristics or said motor and said load.

2. In an electrical follow-up system including an electric motor andamplier means for energizing said motor in response tc control signalsapplied thereto, rectifier means with an input circuit connected to apower input winding of said motor, a source oi bias potential connectedto said rectifier means to establish a threshold of operation thereof,and means :tor applying the output of said rectifier means to the inputcircuit o said amplifier means in opposition to said control signals.

3. in an anti-hunting feedback circuit for electrical follow-up systems,amplifier means, means for deriving a ifeedbaci. voltage to beappliedfto the input circuit of said amplifier means, and means forapplying said voltage to said input circuit, including unidirectionaliyconductive means, a source of bias potential, and means for applyingvoltage from said source to said unidirectionally conductive means toestablish a threshold of operation thereof, whereby said feedbackcircuit operates only when said feedback voltage exceeds a predeterminednite value.

4. The invention as set forth in claim l wherein said variable impedancemeans comprises a pair of electron discharge tubes, transformers havingprimary windings connected in the anode-tocathode circuits of saidtubes, each of said transformers including two secondary windings, allof said secondary windings being connected together to form a bridgecircuit, connections between one conjugate pair of terminals of saidbridge circuit and one input winding of said motor, and connections fromanother conjugate pair of terminals of said bridge circuit to anotherinput circuit of said motor and to said source of electrical energy,whereby said motor input windings are effectively connected in series tosaid source through said variable impedance-means.

5. An electrical follow-up system including an input shaft, an outputshaft, a load coupled to dit said output shaft, means responsive to therelative angular positions of said shafts to produce a pulsating voltagein one of two circuits, depending upon whicliof said shafts lags theother, of a magnitude corresponding to the extent of said-lag, ltermeans connected to said circuits, D.C. amplifier means connected to saidfilter means, variable impedance means connected to be controlled by theoutputs of said amplifier means, an electric motor coupled to saidoutput shaft and connected to a source of electrical energy through saidvariable impedance means, rectifier means with an input circuitconnected to an input circuit of said motor and an output circuitconnected to the input circuits of said lter means, and a source of biaspotential connected to said rectifier means to establish a threshold ooperation thereof.

6. The invention as set forth in claim 5 wherein said variable impedancemeans comprises a pair of electron discharge tubes, transformers havingprimary windings connected in the anodeto-cathode circuits of saidtubes, each oi said transformers including two secondary windings, allof said secondary windings being connected together to form a bridgecircuit, connections between one conjugate pair or" terminals oi saidbridge `circuit and one input winding of said niotor, and connectionsfrom another coniugate pair of terminals of said bridge circuit toanother lnput circuit of said motor and to said source or" electricalenergy, whereby said motor input windings are edectively connected inseries to said source through said variable impedance means.

'7. A motor control system including a .normally balanced bridge circuithaving a pair of output terminals, a motor having two power inputwindings and terminal connections to a source of alternating energy forsaid motor, one of said windings being connected in series between saidterminal connections and said bridge circuit and the other or saidwindings being connected across said output terminals, and electrondischarge means for simultaneously varying the impedances of respectiveconjugate arms of said bridge circuit in opposite directions.

8. A motorcontrol system including a motor having two power inputwindings and terminal connections to a source of alternating energy forsaid motor, a pair of electron discharge devices, means including a pairof transformers each having a primary winding and a pair of secondarywindings, said secondary windings being connected inA a bridge circuithaving a pair of output terminals, one ,of said power input windingsbeing connected in series with said bridge circuit and the other of saidpower input windings being connected across said output terminals andmeans for simultaneously varying the' impedances of said electrondischarge devices respectively in opposite directions.

WILLIAM F. WOLFNER, II.

